214 GREEN AND DRY CROPS. 



ganic matter, the plant itself has elaborated, from 

 oxygen, and hydrogen, carbon, and nitrogen, from 

 whatever source derived. It has decomposed, dur- 

 ing the short period of its growth, as has been alrea- 

 dy pointed out, more silicates and salts, than the air 

 only, could effect during the same period, which being 

 turned in, restore to the soil from which they grew, 

 salts, and silicates in a new form, whose action on 

 vegetation is like that of alkalies. But, powerful as 

 are the effects of green crops, ploughed in, it is the 

 experience of some practical men, that one crop al- 

 lowed to perfect itself and then die where it grew, 

 and then turned in dry, is superior to three turned in 

 green. The whole result is explained by the fact, 

 that dry plants give more geine than green. Green 

 plants ferment, — dry plants decay. A large portion 

 escapes in fermentation as gas, and more volatile pro- 

 ducts are formed, than during decay. The one is a 

 quick consuming fire, the other, a slow mouldering 

 emher, giving off during all its progress, gases, which 

 feed plants, and decompose the silicates of soil. 



289. The power of fertility which exists in the 

 silicates of soil is unlimited. An improved agricul- 

 ture, must depend upon the skill with which this 

 power is brought into action. It can be done only 

 by the conjunction of salts, geine, and plants. Bar- 



